This invention relates to a method and apparatus for forming a pleat in a continuous film web, and more particularly to a method and apparatus for using pressurized air to separate opposing faces and unblock a folded web prior to forming a pleat.
Gusseted plastic bags are typically manufactured from a substantially continuous web of a thermoplastic film which has been folded over onto itself to form a U-folded web. While single ply layers are typical, additional plies of plastic, each comprising one or more thermoplastic materials, may be used to form laminated webs. The edges of the web opposite the U-folded portion may also have complementary closure profiles (i.e., zippers) thereon.
A pleat is formed in the film web when the U-folded edge portion is again tucked or folded inwardly upon itself to form a gusset fold along that edge portion of the web. Numerous gusset configurations are possible including bi-folded and tri-folded gussets. The film web is then heat sealed and severed transversely to form individual gusseted bags. Upon the filling of such gusseted bags with a solid or liquid, the gusset folds expand to form a base of a dimension equivalent to the width of the tucks or folds which were made. Gusseted plastic bags possess an advantage over nongusseted bags in that they are self-supporting and remain upright when filled.
There are many gusseting apparatuses available in the prior art including, for example, Piazze, U.S. Pat. No. 3,618,478, which relates to the gusseting of an open-ended web. A typical apparatus includes a pair of generally aligned, closely-spaced plates positioned inside the film web and contiguous with the interior faces of the folded-over edge portion of the web. Another plate, preferably in the shape of a wheel, is positioned a predetermined distance between the closely-spaced plates but on the exterior surface of the folded-over edge to urge that edge inward to form the pleat in the web which ultimately becomes the gusset.
In the past, problems have arisen in the formation of the pleats in the U-folded webs as those webs were driven through the pleating apparatus. The U-folded film web is provided typically in a condition in which the two opposing faces of the film are flattened against each other due to the nip roll pairs which are used to drive the web through the apparatus. The surfaces of the opposing faces of such folded webs tend to block to each other (i.e., stick together to an extent that they are not easily separated). During high speed formation of the pleat, the blocked web may not open up over the spaced apart plates rapidly enough to permit the proper tuck to be taken in the web by the opposing gusseting wheel. Additionally, the web may hang up on the plates, and misalignment and tears to the web may result.
Accordingly, the need exists in the art to provide a method and apparatus by which the web may be rapidly pleated, but without the misalignment and tearing problems associated with previous pleating methods and apparatuses.